Is it already possible to play FiveM on mobile?
Unfortunately, not yet. There’s a lot of talk about this possibility. With a quick search, you’ll find many videos about FiveM mobile, including APKs. But in reality, FiveM mobile does not exist, and the APK you’ll find is probably for San Andreas Multiplayer with some modifications to make it look like FiveM.

Despite that, it is possible to play GTA San Andreas on your phone by downloading it directly from the Play Store, through Rockstar’s official store. SA-MP is also possible if you prefer to play online with your friends.
But the future of FiveM mobile is not that far away now that FiveM belongs to Rockstar. I think the big companies have already noticed that the future of gaming is on mobile, as was the case with Call of Duty Warzone, which has just been released.
Rockstar would have to think of a way to concentrate all the NUIs on the touchscreen and make it universal for all cities, since in FiveM there are many interactions, such as dancing, arresting, driving, etc. But it’s quite possible.
Besides that, phones would have to be much more powerful than they are now to be able to run GTA V without stuttering, which is already a complicated and expensive task on PC. I’m thinking of something like a ROG Phone 6 or 7.